The overall objective of the project is to investigate the effects of thymectomy in oncogenesis in humans. Specifically, the study is designed in such a way as to investigate whether thymectomy, a procedure that protects against the appearance of breast cancer, leukemias and lymphomas, in experimental animals, may have a similar effect in humans. Goals set for the current year are: 1) The definition and characterization of high cancer risk segments of the myasthenic population through clinical staging, pathology findings and laboratory data. 2) The development of screening methods for identifying the high risk groups in whom early thymectomy may play a preventive role against the appearance of neoplasms. 3) The analysis of differences in cancer risk between the myasthenic populations followed at Mount Sinai Hospital, New York, and those followed at the New End Hospital, London, to further delineate the role that delay in thymectomy for the treatment of myasthenia may have in cancer risk. 4) The investigation of thymic influence in diseases where autoimmunity has been implicated, and that are associated with a high cancer risk and with the presence of thymic germinal centers in the thymus, and/or that are associated with myasthenia gravis. BIBLIOGRAPHIC REFERENCES: Genkins, G., Papatestas, A.E., Horowitz, S.H., Kornfeld, P., Studies in Myasthenia Gravis: Early Thymectomy: Electrophysiological and Pathological Correlations. Am. J. of Medicne 58:517, 1975. Papatestas, A.E., Genkins, G., Kornfeld, P., Horowitz, S.H., Kark, A.E., Transcervical Thymectomy in Myasthenia Gravis Surgery, Gynecology and Obstetrics 140:535-540, 1975.